iommu/vt-d: Use common helper to lookup svm devices

It's common to iterate the svm device list and find a matched device. Add
common helpers to do this and consolidate the code.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210520031531.712333-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20210610020115.1637656-9-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>